One of the common problems of the cam mechanisms is the relatively more rapid wear in comparison to the mechanisms which links are connected by hinged joints.
The main reasons for the intensive wear of cam mechanisms are friction between the cam surface and the element, which is in contact with it; greater contact force transmitted by a very small area between the cam profile and the element in contact with the cam; as well as a break of contact between the cam and the element contacting with its profile and subsequent impact recovery of the contact between them.
Wearing of the cam mechanisms can be reduced to different extent, depending on the requirements to the cam engine and the intended function of the cam mechanism in the given engine.
It is known from EP19379388 a cam engine comprising a housing, at least one cylinder, at least one piston moving in the cylinder, a cylindrical tubular 3D cam with a cam groove on the inner cylindrical surface, which groove is made so that the line forming its cross-section is a straight or concave line whose lower end is located at the side towards the axis of the 3D cam, and at least two equal-mass follower positioned against each other, at least one of which is a working follower, where each follower comprises at least two arms standing at an angle to each other and having main rollers bearing at the free ends of the corresponding arm, and each follower also comprises additional rollers that can move along the axes of the corresponding main rollers, so that each main and additional roller contacts the cam groove. The problem of the intensive wear of the cam mechanism of this known engine is comparatively well settled. In this case each follower is provided not only with main rollers, but also with additional ones, which contact with the profile of the cam groove opposing the cam profile with which the additional rollers of the same follower are in contact. The additional rollers are elastically connected to their respective follower and press it to the cam profile of its adjacent main rollers. This design solution is able to provide constant contact between the followers and their respective cam profiles, if the elastic elements of the additional rollers are hard enough to counteract the effect of the inertia forces of the followers when inertia forces act to interrupt the connection of the followers and the cam. On the other hand, the additional rollers have considerably smaller diameters than the diameters of the main rollers and the cam groove is characterized with constant cross-section, due to which each additional roller will be constantly moving along the axis of its respective main roller when each of them follows the adjacent cam profile. Therefore, each elastic element that presses its corresponding additional roller will constantly shrink and stretch. The shrinking and stretching of the elastic elements will cause unsteady operation of the cam mechanism, which causes altering moments of acceleration and slowdown of the rotation of the main transforming 3D cam. The movement of the known cam mechanism is insofar uneven as the difference between the diameters of the main and additional rollers.
Additionally, in this known piston cam engine there is some loss resulting from the constant shrinking and stretching of the elastic elements, as well as loss resulting from the friction between the additional rollers and the cam profiles. The loss resulted from the friction of the additional rollers in the known engine is due to the fact that they cannot self-adjust while rolling along the corresponding cam profiles, since they only move reciprocally along the axis of the main rollers. As a result friction forces are generated, which cause mechanical loss and wear of the cam mechanism.
Moreover, in this known cam engine, the movement of the additional rollers along the axis of the main rollers is not limited, and thus the use of elastic elements with high hardness and preload is necessary to be applied in order to prevent interruption of contact between the cam and followers when there are inertia forces acting towards their disconnection. When the inertia forces are not aiming to break the contact between the cam and the followers, the additional rollers will be pressed by the elastic elements to their adjacent cam profile with unnecessarily large forces, leading to a faster wear of the cam profile.
This known patent EP19379938 also discloses laws of motion of the piston cam engine, due to which its operation is improved. These laws, however, do not completely guarantee the contact between the followers and the main transforming cam.